Steel pipe welding method

Abstract

An improved welding method for welding an inner seam of a longitudinally welded steel pipe along an inner groove by welding electrodes held by a boom which is supported by a tracing roller moving along the inner groove of the steel pipe. According to the invention, at least one metal plate is urged against at least one end of the steel pipe after tack welding the seam on an opposite side of the inner groove of the steel pipe to be welded. Lateral angular deformations of the end of the steel pipe are prevented on both sides of the seam. Such deformations are due to the load of the boom when the tracing roller leaves the end of the steel pipe for the metal plate. Thus, the invention provides for prevention of hot cracking at the end of the pipe. Moreover, according to the invention, portions of the steel pipe on both sides of the distal end of the weld bead, at the end of the pipe, are heated to cause expansion displacements of the heated portions directing toward the center of the weld bead, or high temperature portions of the steel pipe, after a heat source for the seam welding has passed therethrough, are cooled, thereby reducing tearing forces acting upon the weld bead so as to prevent more effectively the hot cracking at the end of the pipe.

What is claimed is: 
     
       1. A longitudinally welded steel pipe welding method for welding an inner seam by welding electrodes held by a boom which is supported by a preceding tracing roller moving along an inner groove of a steel pipe, comprising steps of urging at least one metal plate against at least one end of the steel pipe at said groove after tack welding said seam on an outside of the steel pipe on an opposite side of said inner groove at least at the end of the steel pipe, and preventing lateral angular deformations or changing of the lateral angular deformations of the end of the steel pipe on both sides of a weld bead due to a load of said boom when said preceding tracing roller leaves said end of the steel pipe for said metal plate. 
     
     
       2. A method as set forth in claim 1, wherein the outside of the steel pipe on the opposite side of said inner groove at least at the end of said steel pipe is supported by a support surface and said metal plate is supported by metal plate support means adjustable in height for preventing said lateral angular deformations or changing of said lateral angular deformations of the end of the steel pipe on both the sides of the weld bead. 
     
     
       3. A method as set forth in claim 1 wherein a relative movement between said metal plate and the end of the steel pipe is restrained by connecting means for preventing said lateral angular deformations or changing of the said lateral angular deformations of the end of the steel pipe on both the sides of the weld bead. 
     
     
       4. A method as set forth in claim 1, wherein said metal plate is supported by metal plate support means adjustable in height, and in addition to said preceding tracing roller a rear tracing roller is provided to transmit a load of said boom to the end of the steel pipe after said preceding tracing roller leaves the end of the steel pipe for preventing said lateral angular deformations or changing of said lateral angular deformations of the end of the steel pipe on both the sides of the weld bead. 
     
     
       5. A longitudinally welded steel pipe welding method for welding an inner seam by welding electrodes held by a boom supported by a preceding tracing roller moving along an inner groove of a steel pipe, comprising steps of urging at least one metal plate against at least one end of the steel pipe at said groove, and heating portions of the steel pipe on both sides of at least a distal end of a weld bead at the end of the steel pipe to cause expansion displacements of the heated portions directing toward a center of said weld bead for preventing lateral angular deformations or changing of said lateral angular deformations of the end of the steel pipe on both sides of a weld bead due to a load of said boom when said preceding tracing roller leaves the end of the steel pipe for said metal plate. 
     
     
       6. A method as set forth in claim 5, wherein portions spaced from and on both sides of the weld bead of the end of the steel pipe are linearly heated along a movement of a heat source for welding. 
     
     
       7. A method as set forth in claim 5, wherein portions of the steel pipe as near as possible to and on both sides of a rearmost end of a crater are heated. 
     
     
       8. A method as set forth in claim 5, wherein an outside of the steel pipe on an opposite side of said inner groove at least at the end of the steel pipe is supported by a support surface and said metal plate is supported by metal plate support means adjustable in height for preventing said lateral angular deformations or changing of said lateral angular deformations of the end of the steel pipe on both the sides of the weld bead. 
     
     
       9. A method as set forth in claim 5, wherein a relative movement between said metal plate and the end of the steel pipe is restrained by connecting means for preventing said lateral angular deformations or changing of the deformations of the end of the steel pipe on both the sides of the weld bead. 
     
     
       10. A method as set forth in claim 5, wherein said metal plate is supported by metal plate support means adjustable in height, and in addition to said preceding tracing roller a rear tracing roller is provided to transmit a load of said boom to the end of the steel pipe after said preceding tracing roller leaves the end of the steel pipe for preventing said lateral angular deformations or changing of said lateral angular deformations of the end of the steel pipe on both the sides of the weld bead. 
     
     
       11. A longitudinally welded steel pipe welding method for welding an inner seam by welding electrodes held by a boom supported by a preceding tracing roller moving along an inner groove of a steel pipe, comprising steps of urging at least one metal plate against at least one end of the steel pipe at said groove, and cooling high temperature portions of the end of the steel pipe after a heat source for the seam welding has passed therethrough for preventing lateral angular deformations or changing of said lateral angular deformations of the end of the steel pipe on both sides of a weld bead due to a load of said boom when said preceding tracing roller leaves the end of the steel pipe for said metal plate. 
     
     
       12. A method as set forth in claim 11, wherein said high temperature portions are cooled by a gas-cooling device for jetting a cooling gas selected from air, mist, nitrogen, argon and CO 2 . 
     
     
       13. A method as set forth in claim 11, wherein said high temperature portions are cooled by a box-shaped cooling device filled with a refrigerant. 
     
     
       14. A method as set forth in claim 11, wherein an outside of the steel pipe on an opposite side of said inner groove at least at the end of the steel pipe is supported by a support surface and said metal plate is supported by metal plate support means adjustable in height for preventing said lateral angular deformations or changing of said lateral angular deformations of the end of the steel pipe on both the sides of the weld bead. 
     
     
       15. A method as set forth in claim 11, wherein a relative movement between said metal plate and the end of the steel pipe is restrained by connecting means for preventing said lateral angular deformations or changing of the deformations of the end of the steel pipe on both the sides of the weld bead. 
     
     
       16. A method as set forth in claim 11, wherein said metal plate is supported by metal plate support means adjustable in height, and in addition to said preceding tracing roller a rear tracing roller is provided to transmit a load of said boom to the end of the steel pipe after said preceding tracing roller leaves said end of the steel pipe for preventing said lateral angular deformations or changing of the deformations of the end of the steel pipe on both the sides of the weld bead. 
     
     
       17. A method as set forth in claim 11, wherein said high temperature portions are cooled by a box-shaped cooling device provided with a piping for circulating cooling liquid.